1. Field of the Invention
This invention relates to a multilayer ceramic chip capacitor and more particularly, to a multilayer ceramic chip capacitor having improved dielectric layers.
2. Prior Art
Multilayer ceramic chip capacitors are generally fabricated by layering an internal electrode-forming paste and a dielectric layer-forming paste by sheeting, printing and similar techniques followed by integral co-firing.
Generally the internal electrodes have been formed of Pd and Pd alloys although the use of relatively inexpensive Ni and Ni alloys instead of expensive Pd is expanding.
Internal electrodes of Ni and Ni alloys are oxidized if fired in ambient air.
In this regard, after binder removal, firing is typically carried out at an oxygen partial pressure which is lower than the equilibrium oxygen partial pressure between Ni and NiO.
To consolidate the dielectric material in this case, it is a common practice to add SiO.sub.2 sintering aid.
Another approach for preventing dielectric layers from lowering their insulation resistance due to reduction is Mn addition or Ca replacement.
Multilayer chip capacitors having internal electrodes of Ni or Ni alloys, however, suffer from the problems of an extremely short life of insulation resistance and low reliability as compared with multilayer chip capacitors having internal electrodes of Pd which are prepared by firing in ambient air.
Nevertheless, these problems were almost overcome by the multilayer ceramic chip capacitor which the inventors proposed and in which a dielectric material containing a dielectric oxide having a specific composition having added thereto a specific amount of at least one member selected from the group consisting of oxides of Y, Gd, Tb, Dy, Zr, V, Mo, Zn, Cd, Tl, Sn and P and/or compounds which will convert to the oxides upon firing, and an internal electrode-forming material in the form of Ni or Ni alloy are layered and fired (see Japanese Patent Application Kokai No. 133116/1991).
That is, it was found that by adding yttrium or similar elements, an about 2 to 10 times extended life and fairly improved reliability are obtained as compared with prior art chip capacitors free of such elements.